Mechanical actuator with permanent magnet



y 1966 E. R. PERRY MECHANICAL: ACTUATOR WITH PREMANENT MAGNET Filed Oct.

M ma 3 WWW United States Patent This invention relates to mechanical actuators, more specifically to an actuator for a device such as an electrical switch.

In several applications it would be advantageous to I separate the contacts of a switch very rapidly; for example, in interrupting D.C. circuits with the aid of resonant circuits the capacitors and inductors could be made smaller if the switch were faster opening. In alternating current switching, it would be advantageous to open the contacts of a switch just prior to or exactly at the zero crossing of the current wave form; as is well known, separating the contacts at current zero prevents an are from forming between the contacts and thereby interrupts the circuit faster and also reduces contact erosion. To interrupt at current zero very fast contact separation is required because a mechanical delay of only a millisecond is, a significant portion of a period of a sixty cycle sinusoid. A faster opening switch would simplify predicting a zero crossing and it would help to prevent striking an are after the zero crossing. An object of this invention is to provide an improved switch that is fast enough for practical D.C. interruption and for zero current interruption in an A.C. system.

The switch actuator of this invention has means such as springs or a gas driven piston that provides stored energy for driving the contacts open, and it has a permanent magnet that latches it in its closed position when the switch is mechanically reclosed. A coil in the magnetic circuit of the permanent magnet is pulsed to oppose the permanent magnet field and release the magnetic latch.

The permanent magnet has the advantage that it provides a hold-ing force without requiring power, as an electromagnet would. However, a permanent magnet presents several problems. For example, some permanent magnet materials with many desirable characteristics for this actuator undesirably undergo changes in their holding I force with changes in temperature. This seriously complicates the actuator design because the minimum available holding force must be greater than the stored opening force, and the tripping pulse must be high enough to release the highest holding force. One object of this invention is to provide a new and improved mechanical actuator in which the force provided by a permanent magnet is kept satisfactorily uniform in spite of environmental changes. In the actuator that will be described in detail, a nonpermanent magnet element with a rather stable saturation flux density is positioned in the magnetic circuit of the permanent magnet. The permanent magnet is made to provide enough magnetic field intensity under the most adverse expected conditions to saturate the nonpermanent magnet element. The stable saturation value of the nonpermanent magnet element thus establishes a stable holding force value.

Another problem with some permanent magnet operated devices is that a current pulse intended only to oppose the magnetic field may undesirably desaturate the permanent magnet. Another object of this invention is to provide a new and improved permanent magnet device with means to isolate the permanent magnet from the release pulse for current values above the value required to release the device.

It is diflicult to construct a device of magnetic mate- 3,253,098 Patented May 24, 1966 rial that responds fast to a current pulse; eddy currents that form in the material oppose changes in flux. It is Well known to make such devices of highly resistive material such as powdered iron or thin laminations. One of the disadvantages of such materials is that the insulating material adds to the mass of the moving magnetic parts of the actuator and thereby slows its response. Another disadvantage is that many of these materials are difficult to fabricate into the shapes desirable for the actuator. The mechanical actuator of this invention has its movable magnetic parts and preferably some of its stationary magnetic parts made of a material that has a high permeability in relation to its density. This material may also have a high conductivity. The actuator has its release coil located in a region of highly resistive magnetic material; when the coil is pulsed, the flux changes rapidly in the highly resistive region and also in the region where the magnetic holding force is developed. Consequently, the actuator releases very rapidly when its coil is pulsed.

The drawing and the detailed description of this invention will suggest other problems in providing a suitable switch actuator and will suggest the corresponding features and advantages of the switch actuator of this invention.

The drawing FIG. 1 is a sectional view of a switch actuator of this invention; and

FIG. 2 is a sectional view of the 'switch actuator taken along line IIII of FIG. 1.

The actuator The switch actuator 10 of FIG. 1 is adapted to move the movable contact 11 of the vacuum switch12 along a straight line 13 to open or close the switch. Actuator 10 is substantially rotationally symmetrical about line 13; it has a movable assembly 14 that is reciprocated along line 13, and it has a stationary structure 15 that surrounds the movable assembly. A stored energy device 17 is provided to drive the movable assembly 14 outward from the stationary structure 15 to open switch 12. Device 17, illustrated as a spring, may comprise alternatively for example a charge of compressed gas contained Within the actuator. Suitable means, not shown, is provided for recl-osing switch 12; this may comprise a piston operated by compressed gas. When movable assembly 14 is reset to the position of FIG. 1, spring 17 is compressed and the movable assembly is held closed by the actuator of a permanent magnet 20 on a magnetic clapper 21 of movable assembly 14. To open switch 12, coil 22 that is located to oppose the magnetic attraction of permanent magnet 20 is pulsed. Thus, without any mechanically moving parts, springs 17 are released to drive the switch open.

The components of the magnetic holding circuit of stationary structure 15 will be described in detail first because they mechanically support the other elements of the actuator. Permanent magnet 20 is shaped in a ring to provide an opening which parts of the movable assembly pass through. It is magnetized in its axial direction; with this magnetic orientation, the pole faces 23, 24 can easily be made flat to mechanically fit closely with other elements that form the magnetic holding circuit. These other elements are shaped to establish a narrow air gap 25 where the magnetic attracting force is developed.

One of these other elements is a part 27 made of a magnetic material that has a saturation flux density that is sufficiently well defined (with respect to the magnetizing force and environmental conditions) to provide a spaced apart sufiiciently for coil 22 to be positioned between them. Parts 28, 29 have suitably shaped surfaces to fit mechanically with other elements of the actuator. In the preferred embodiment shown in the drawing, element 27 is a single piece with a coil receiving groove formed between portions 28, 29.

Stationary assembly 15 also includes elements 31, 32, 33 of any suitable material that are arranged to cooperate with elements 20, 27 to define the magnetic circuit. Element 30 is generally disk shaped with a fiat surface 38 shaped to fit closely against pole face 24 of magnet 20, a flat surface 39 shaped to fit closely against a corresponding surface 40 of element 31, and a center opening 41 that parts of movable assembly 14 slide through. Elements 31, 32 are shaped to form the cylindrical sides of the actuator and to form one generally fiat end 44 and. are provided with suitable surfaces 45, 46 for mechanically fitting closely with corresponding surfaces of element 27. End 44 has a radially inwardly facing cylindrical surface 47 where element 32 is slightly spaced from element 33; an outer flat surface 48 that forms a seat for clapper 21 (end 44 also has an outer annular groove 50 that holds spring 17 as will be explained later). Element 33 extends from the radially inner side of air gap 25 to the other pole face 23. Element 33 is shaped to have an outer cylindrical surface 52 forming one side of air gap 25; a flat surface 53 that forms a seat for clapper 21; an inner cylindrical opening 55 through which some of the movable components 14 slide; and a flat surface 56 that closely fits against pole face 23.

Permanent magnet 20 and magnetic circuit elements 30, 31, and 32 are held together by suitable screws 57 and nonmagnetic spacers 58.

As FIG. 1 shows, the area'of the seats 48 and 53 may be less than the magnetic cross section of other parts of the magnetic circuit to increase the flux density in the air gap between the seats and clapper 21.

Coil 22 is wound in the circumferential groove of element 27. Its two leads 61, 62 are brought outside stationary structure 15 through a depression in the edge of element 27 and a hole 63 in spacer 58. Coil 22 is suitably supported to with-stand the mechanical forces associated with a high current pulse.

Movable assembly 14 comprises clapper 21, a rod 65 that has one end suitably connected to the vacuum switch movable contact 11, and has its other end attached to the clapper 21 by, means of a screw 66. Prefer-ably the end of rod 65 is provided with a flange 67, and. a com pressible gasket 68 is located between flange 67 and clapper 21. Turning screw 66 makes small changes in the position of contact 11. All of these part-s are made as light as possible. For example, clapper 21 is made thin in its center portion where it does not conduct flux. It is made of a solid magnetic material to provide a low space factor. Rod 65 may have a hollow center and is preferably made of aluminum to be light weight (and to prevent it from magnetically coupling elements and 31 of the holding circuit).

Clapper 21 has a radially outer portion that is shaped to fit closely on surfaces 48 and 53, and enough magnetic material is located in this region of clapper 21 to conduct the flux for the necessary holding force. The outer rim 69 of clapper 21 hangs over the annular groove 50 where spring 17 is positioned. Spring 17 is compressed when the clapper is closed as FIG. 1 shows and urges clapper 21 outward in the contact opening direction.

Operation When clapper 21 is held against seats 48 and 53 and coil 22 is deenergized, the magnetic field of permanent magnet 20 attracts clapper 21 and holds the switch closed. The force between clapper 21 and stationary structure 15 is a function of the area of the seats 48, 53 and the square of the flux density in the region of the seats.

Preferably, permanent magnet 20 is made to provide at least enough flux when the magnetic circuit is closed by clapper 21 to saturate element 27. Thus, ring 27 regulates the flux density and the holding force as changes in temperature or other factors change the magnetic characteristics of permanent magnet 20. The saturation flux density and the area of element 27 are chosen to provide a suitable holding force on clapper 21.

When coil 22 is pulsed, it changes the H field in the region of element 27; it aids permanent magnet 20 in one part 28 or 29 and opposes the permanent magnet on the other part 28 or 29. Suppose that coil 22 is pulsed in the polarity to oppose the H field in part 28 and aid the H field in part 29. Because inner part 29 is either near saturation or is saturated when the clapper 21 is closed, the strengthened H field in this regiondoes not add significantly to the flux density in this region or in clapper 21. In opposing the H field in the radially outer part 28, coil 22 reduces the flux density in this region and in clapper 21. When the ampere turns of coil 22 counterbalance the magnetic force of permanent magnet 20, the flux density in the radially outer part 28 is zero and permanent magnet 20 provides approximately 50% of the usual flux density in clapper 21. With this reduction in flux density, the magnetic holding force falls from to only about 25%. The magnetic circuit components and spring 17 are constructed so that this reduction in holding force is enough to release the magnetic latch to cause spring 17 to open switch 11.

One significance of the radially inner portion 29 of element 27 is that it controls the minor hysteresis loop that permanent magnet 20 operates on. Suppose that a very high current amplitude pulse is applied to coil 22.

Except for portion 27 such a current pulse might demagnetize permanent magnet 20. Notice that with respect to coil 22, inner saturable portion 28 is magnetically in parallel with permanent magnet 20.

When inner portion 29 is not saturated, it tends to divert -flux associated with coil 22 from flowing in the magnetic circuit of permanent magnet 20 because the path of permanent magnet 20 is longer and thus has -a higher reluctance than the parallel path of inner portion 29. The maximum flux associated with coil 22 is the saturation level of either the outer or the inner portion 28, 29. Since flux flows only in closed loops, coil 22 cannot saturate the radially inner portion 29 and demagnetize permanent magnet 20 because this is more flux than the radially outer portion 28 can conduct.

When coil 22 is pulsed in the opposite polarity a corresponding operation takes place to release clapper 21.

Because the actuator is fast opening it is particularly useful for operating switch 12 to open at a predetermined point in an electrical wave form of the system the switch is connected in. Coil 22 is pulsed ahead of this predetermined point by the time delay of the actuator and switch. In an electrical system with a sinusoidal wave form, simple phase shifting circuits can provide an appropriately leading signal to trigger coil 22.

From the single embodiment of the invention that has been described in detail, those skilled in the art will recognize variations in detail within the spirit of the invention and the scope of the claims.

Having now particularly described and ascertained the nature of my said invention and the manner in which it is to be performed, I declare that what I claim is:

1. An actuator for moving a device such as a movable contact element of a circuit interrupter, comprising,

a clapper of magnetic material adapted to move in a predetermined path and having means for being connected to move the device in a corresponding path,

a permanent magnet,

magnetic means connecting said permanent magnet in magnetic circuit with said clapper to attract said clapper with a predetermined force at one end of its predetermined path, said magnetic means including a portion that has sufficient electrical resistance and low permeability to provide rapid changes in the flux density when said portion is excited by a current pulse, the remainder of said magnetic means in said magnetic circuit comprising material having a lower electrical resistance than said portion,

means positioned between said clapper and said permanent magnet providing a force less than said predetermined force tending to move said clapper toward the other end of its path,

a conductor positioned adjacent said resistive portion and being connected to provide a magnetic force in said portion to oppose the magnetic eflect of said permanent magnet with suflicient force to release said clapper when said conductor is pulsed with a predetermined magnitude of current, and

said portion having first and second parts, one of which is saturable in response to a current of said predetermined magnitude in said conductor.

'2. An actuator according to claim l in which said first and second parts are positioned with respect to said conductor to provide opposite magnetic forces in said magnetic circuit when excited by said conductor current, the one of said parts in which said magnetic force is aiding said permanent magnet being saturable to limit the flux in said part.

3. An actuator according to claim 2 in which both of said parts are saturable but at diiferent values of magnetic flux.

4. An actuator according to claim 2 in which both of said parts are saturable at substantially equal values of magnetic flux.

5. An actuator according to claim 4 in which said clapper has a region composed substantially exclusively of magnetic material having a lower reluctance than said saturable portion for conducting magnetic flux when said clapper is at said one end of its predetermined path.

6, An actuator according to claim 4 in which the holding flux provided by said permanent magnet varies within -a predetermined range with environmental changes, both said parts being formed to magnetically saturate at the maximum flux value of said range to establish a uniform holding force. I

References Cited by the Examiner UNITED STATES PATENTS 2,435,425 2/ 1948 Cunningham 317-171 2,579,723 12/ 1951 Best 317-171 2,915,681 12/1959 Troy 317-171 3,040,219 6/ 1962 Conrad 317-172 3,129,308 4/ 1964 Yokayama et a1 200--l'44 BERNARD A. GILHEANY, Primary Examiner.

I. J. BAKER, Assistant Examiner. 

1. AN ACTUATOR FOR MOVING A DEVICE SUCH AS A MOVABLE CONTACT ELEMENT OF A CIRCUIT INTERRUPTER, COMPRISING, A CLAPPER OF MAGNETIC MATERIAL ADAPTED TO MOVE IN A PREDETERMINED PATH AND HAVING MEANS FOR BEING CONNECTED TO MOVE THE DEVICE IN A CORRESPONDING PATH, A PERMANENT MAGNET, MAGNETIC MEANS CONNECTING SAID PERMANENT MAGNET IN MAGNETIC CIRCUIT WITH SAID CLAPPER TO ATTRACT SAID CLAPPER WITH A PREDETERMINED FORCE AT ONE END OF ITS PREDETERMINED PATH, SAID MAGNETIC MEANS INCLUDING A PORTION THAT HAS SUFFICIENT ELECTRICAL RESISTANCE AND LOW PERMEABILITY TO PROVIDE RAPID CHANGES IN THE FLUX DENSITY WHEN SAID PORTION IS EXCITED BY A CURRENT PULSE, THE REMAINDER OF SAID MAGNETIC MEANS IN SAID MAGNETIC CIRCUIT COMPRISING MATERIAL HAVING A LOWER ELECTRICAL RESISTANCE THAN SAID PORTION, MEANS POSITIONED BETWEEN SAID CLAPPER AND SAID PERMANENT MAGNET PROVIDING A FORCE LESS THAN SAID PREDETERMINED FORCE TENDING TO MOVE SAID CLAPPER TOWARD THE OTHER END OF ITS PATH, A CONDUCTOR POSITIONED ADJACENT SAID RESISTIVE PORTION AND BEING CONNECTED TO PROVIDE A MAGNETIC FORCE IN SAID PORTION TO OPPOSE THE MAGNETIC EFFECT OF SAID PERMANENT MAGNET WITH SUFFICIENT FORCE TO RELEASE SAID CLAPPER WHEN SAID CONDUCTOR IS PULSED WITH A PREDETERMINED MAGNITUDE OF CURRENT, AND SAID PORTION HAVING FIRST AND SECOND PARTS, ONE OF WHICH IS SATURABLE IN RESPONSE TO A CURRENT OF SAID PREDETERMINED MAGNITUDE IN SAID CONDUCTOR. 